fanotify: allow userspace to override max marks (ac7e22dc) · Commits · 戴 / test

Some fanotify groups, especially those like AV scanners, will need to place lots of marks, particularly ignore marks. Since ignore marks do not pin inodes in cache and are cleared if the inode is removed from core (usually under memory pressure) we expose an interface for listeners, with CAP_SYS_ADMIN, to override the maximum number of marks and be allowed to set and 'unlimited' number of marks. Programs which make use of this feature will be able to OOM a machine. Signed-off-by:

Eric Paris <eparis@redhat.com>

fs/notify/fanotify/fanotify_user.c

+8 −1

Original line number	Diff line number	Diff line
		@@ -707,7 +707,14 @@ SYSCALL_DEFINE2(fanotify_init, unsigned int, flags, unsigned int, event_f_flags)
		group->max_events = FANOTIFY_DEFAULT_MAX_EVENTS;
		}

		if (flags & FAN_UNLIMITED_MARKS) {
		fd = -EPERM;
		if (!capable(CAP_SYS_ADMIN))
		goto out_put_group;
		group->fanotify_data.max_marks = UINT_MAX;
		} else {
		group->fanotify_data.max_marks = FANOTIFY_DEFAULT_MAX_MARKS;
		}

		fd = anon_inode_getfd("[fanotify]", &fanotify_fops, group, f_flags);
		if (fd < 0)

include/linux/fanotify.h

+3 −1

Original line number	Diff line number	Diff line
		@@ -32,9 +32,11 @@
		FAN_CLASS_PRE_CONTENT)

		#define FAN_UNLIMITED_QUEUE 0x00000010
		#define FAN_UNLIMITED_MARKS 0x00000020

		#define FAN_ALL_INIT_FLAGS (FAN_CLOEXEC \| FAN_NONBLOCK \| \
		FAN_ALL_CLASS_BITS \| FAN_UNLIMITED_QUEUE)
		FAN_ALL_CLASS_BITS \| FAN_UNLIMITED_QUEUE \|\
		FAN_UNLIMITED_MARKS)

		/* flags used for fanotify_modify_mark() */
		#define FAN_MARK_ADD 0x00000001

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